Efficient Bending with Electric Press Brakes By Lynn Stanley (Reposted from the FF Journal)
Comeq’s electric press brake reduces material handling and setup times for fabricators
October 2011 – Despite a fluctuating global economy and on-again, off-again gains in U.S. manufacturing, Boltswitch Inc., Crystal Lake, Ill., and CR Metal Products, St. Louis, are finding ways to raise profit margins. Their strategies included investing in a Safan electric press brake. The move helped the two companies squeeze greater efficiencies from their bending operations with some surprising results.
Boltswitch designs and manufactures bolted pressure contact switches and a variety of other products primarily for the electric industry. Switch ratings range from 400 amps to 6,000 amps with voltage ratings of up to 600 V.
To maintain part quality, the manufacturer builds its products and components in-house. Fabrication of some parts, like operator housings, was consuming production time because of older equipment. The operator housing assembly, a box-shaped mechanism for opening and closing electrical switches, starts life as a flat sheet of 11-gauge or 7-gauge steel. A turret press fabricates blanks 28 in. wide by 12 in. long. The blank is then bent or folded into a box approximately 16 in. wide by 6 in. high and 41⁄2 in. deep.
“We were bottom bending the part on 1960s and 70s mechanical press brakes,” says Mark Kingston, CNC technician for Boltswitch. “The bend profile requires eight 90-degree angles. The press operator would make the first bend, put the part down on a 12-ft.-long table, take another blank and make the first bend, repeating this process for all eight bends.”
Looking to reduce material handling and improve part accuracy, Boltswitch considered several CNC press brakes. “For a manufacturer that makes switches to turn electricity on and off, the Safan electric press brake just made sense,” Kingston says. Boltswitch sourced the press brake from Comeq Inc., White Marsh, Md. Comeq is a metal-fabrication specialist representing lines for press brakes and shears; angle, plate and light plate bending rolls; ironworkers and electric press brakes.
The press brake was installed in August 2011, and within the first week, the manufacturer used the machine to bend its operator housings. “One hundred parts used to take a week to complete,” Kingston says. “We ran the same 100 parts on the electric press brake using air bending in about five hours. We saved a week’s worth of labor and achieved a consistent 90-degree bend with each part. That type of return on investment is phenomenal. I estimate we’ll save about a month a year on that part run in labor. Most importantly, the first part becomes a finished part and can be checked for accuracy before beginning to form a second part.”
The manufacturer is able to stage parts like the operator housing across the length of the bed, a feature that gives the press operator the ability to perform all eight bends in one operation. “You can’t off-center load on a mechanical press brake,” says John Dittus, Safan product manager for Comeq. “Off-center loading allows manufacturers to consolidate multiple tooling setups or processes into one machine to improve efficiency and reduce costs associated with material handling.”
Bending smaller parts also is easier and more efficient. The manufacturer’s mechanical press brake required press operators to push a treadle to maneuver the ram, creating a lot of legwork. The electric press uses a light curtain to read the operator’s hand when it breaks the beam, permitting manipulation and bending of the part without touching the pedal. “We have just scratched the surface in terms of our bending capabilities with this press brake, but we already feel like we went from ‘The Flintstones’ to ‘The Jetsons’ overnight,” Kingston says.
As a job shop, CR Metal Products, St. Louis, was looking at business models that could enhance its production efficiencies. The company opted for quick-response manufacturing instead of traditional lean methods because the approach fit its job shop profile. “How do you kanban parts you don’t know if you will ever make again?” asks Mark Chadwick, vice president of operations for CR Metal Products.
The job shop provides a turnkey solution for custom metal fabrication, powder coating and silkscreen printing. Able to design and process complex parts in aluminum and galvanized, stainless and cold-rolled steel, its customer base includes the HVAC, agriculture, electrical enclosures and electronics housings markets and parts for heavy-equipment OEMs.
The first step was to move equipment to create multifunctional cells capable of completing fabrication and eliminating work-in-process. Volumes also were growing for smaller components 8 in. by 18 in. that required formed features such as knock outs. “The parts’ envelope wasn’t suited for fabrication with our automated technology,” Chadwick says. “As volume for these parts continued to grow, coupled with creation of the cells, we found ourselves without as many high-precision press brakes as we needed.”
Chadwick was attracted to the Safan press brake because it was electric and offered the versatility of eight axes, but he had reservations about air bending. “I didn’t feel you could get the same precision with air bending as you could with coining. I felt coining was the best approach for producing accurate 90-degree bends, and the method took material variation out of the equation. Seeing the press brake in operation threw all my old theories out the window,” he says.
For Chadwick, the demonstration occurred during an unlikely set of circumstances. Installed in June 2011, the press brake still was considered untried. When a customer called requiring same-day turnaround for an enclosure that consisted of approximately 30 unique parts, the operator chose to run the job on the new electric press brake. The bend profile called for 30-degree and 90-degree bends, ribs, offsets and hems. Extra parts were not available for setup, and there was not enough time to cut extra parts if mistakes were made during bending.
“I checked on the progress of the job because the customer needed to see a completed unit before leaving town and realized my operator had picked the toughest job with the tightest turnaround to run on the new machine,” says Chadwick. “He knocked out a sample, and it was right the first time. We met the deadline. The repeatability on the electric press brake was phenomenal. Setup was much faster, and we maintained straight bends without the use of crowning, crowning adjustments or shims.”
The electric press brake does not rely on crowning to produce accurate bends. Conventional press brakes are built typically with a cylinder on either end of the machine with a crown cut into the bed for consistent bending during compression. The bending force of the electric press brake comes from multiple points and is spread evenly throughout the bed length rather than being generated from two localized points on either end of the machine.
Without the need to make crown or ram adjustments prior to bending, the time normally associated with setup and other prep work is eliminated. “The press brake’s E-Bend-S feature automatically measures material thickness and inputs the data into the machine,” says Dittus. “Thickness tolerance can dramatically affect the bend angle. From the point of measurement to applying automatic correction during bending, the whole process takes about 21⁄2 seconds. This means parts will be accurate the first time.”
For Chadwick, the proof is in his team’s choice of press brakes. “If we have a hot job, the team will choose the electric brake every time because setup on the other machines is so time consuming. With the electric press brake, our operator knows he can pull a setup out if he has to wait five minutes for parts, run a hot job and then throw the tools back in and bend a good part on the first try. This kind of confidence gives us the flexibility to run our shop true to the principles of quick-response manufacturing.”